SPECTROSCOPIC STUDY OF ALN FILM FORMATION BY THE SEQUENTIAL REACTION OF AMMONIA AND TRIMETHYLALUMINUM ON ALUMINA

Aluminum nitride is grown on an alumina substrate by several sequentia l exposures to trimethyl aluminum and ammonia. Broad similarities are evident between the chemistry in this case and that found for the reac tion between trimethylaluminum and water except that temperatures of i n excess of 500 K are required to form AlN layers whereas alumina is f ormed at room temperature. It is found, using infrared spectroscopy to examine the surface species formed during repeated sequential adsorpt ion of trimethylaluminum and ammonia, that trimethylaluminum initially reacts to form an adsorbed dimethylaluminum species. This reacts with ammonia to initially form a Lewis acid-base adduct which subsequently reacts to form bridging and terminal NH2 species. The first methyl gr oup in the adsorbed species is found to be more reactive than the seco nd, an effect that was also noted for reactions with water. The ultima te formation of AlN films by several sequential exposures to trimethyl aluminum and ammonia is confirmed using X-ray photoelectron spectrosco py and gravimetrically by weighing the samples after several trimethyl aluminum and ammonia exposure cycles.